The immune system plays a critical role in the pathogenesis of neoplasia. The shortcomings of the immune system in this disorder can be broadly considered as the failure to develop a sufficiently potent response to a deleterious target. Standard medical treatments for cancer, including chemotherapy, surgery, and radiation therapy, have clear limitations with regard to both efficiency and toxicity. While prevention of primary and/or metastatic cancer would be ideal, these approaches typically have met with little success. New strategies which stimulate the immune system to mount a successful attack on neoplastic cells are greatly needed.
It is known that the presence of a neoplasm may elicit a cellular immune response. For example, blood and tumor infiltrates from melanoma and renal carcinoma patients contain circulating cytotoxic precursor cells with specific reactivity for autologous melanoma (see, e.g., Darrow et al. (1989) J. Immunol. 142:3329-35; Crowley et al. (1991) J. Immunol. 146:1692-9; Crowley et al. (1992) Cancer Res. 52:394) and renal carcinomas (see, e.g., Belldegrun et al. (1988) Cancer Res. 42:206-214; Radrizzani et al. (1989) Cancer Immunol. Immunother. 28:671; Belldegrun et al. (1990) Cancer Immunol. Immunother. 31:1; Ikemoto et al. (1992) Cancer Immunol. Immunother. 34:289; Koo et al. (1991) J. Immunol. Ther. 10:347; Alexander et al. (1990) J. Cancer. 45:119). This cellular response may result from the presence of tumor rejection antigens on the surface of tumor cells (see, e.g., U.S. Pat. No. 5,763,155). However, a serological response to the tumor has been difficult to demonstrate.
Several hypotheses for this inability exist, such as that tumor cells are poor antigen-presenting cells, have low or absent MHC molecules expressed on the cell surface, secrete suppressor factors, or that T-cell receptor (TCR) engagement by the tumor antigens without a costimulatory signal induces anergy. The inability of the immune system to elicit an antibody response may also or alternatively result, in part, from the inability of the immune system to distinguish a neoplastic cell from a normal, non-cancerous cell due to the possession of common surface antigens.
Immunotherapy for cancer is based on the premise that the immune system can be activated or manipulated to recognize and eradicate tumors. Systemic immune responses to tumor cells have been shown to be capable of mediating tumor rejection in animal models and in some patients with cancer (Joannides, et al. (1993) Immunol. 37:413-442; Urban et al. (1993) Ann. Rev. Immunol. 10:617-644; Van der Bruggen, et al. (1991) Science 254:1643-1647; Porgador, et al. (1994) Nat. Immunol. 13:113-130; and Pardoll (1993) Curr. Op. Immunol. 5:719-725).
Approaches to activate the immune system have included the use of vaccines. A vaccine is a way of delivering an antigen to the immune system such that the immune system recognizes the antigen as foreign and rejects or destroys any cells bearing that antigen. Proliferation-incompetent allogeneic or autologous tumor cells have been used as vaccines. For example, polyvalent allogeneic melanoma vaccines have been reported to improve survival of patients with metastatic melanoma (Sanda et al. (1994) J. Urol. 151:622-628). In addition, vaccines derived from allogeneic melanoma tumor cell lines have not been associated with clinically significant toxicity when given alone (Dranoff et al. (1993) Proc. Natl. Acad. Sci. (USA) 90:35-39). However, such immunity has been short-lived.
Autologous cancer cells also have been used as vaccines to augment anti-tumor immunity (Oettgen et al. in Biologic Therapy of Cancer (1991), Devita et al., eds., 5 Lippincott Co., pp. 87-119). Such vaccines, in theory, should be very powerful because they are highly specific for the tumor from which the vaccine was prepared. However, the immunogenicity of cancer cells is generally too weak to elicit a pronounced immune reaction sufficient to overcome the disease, perhaps due to the theories described above. Patient responses to these “raw” vaccines have generally been only partial and relatively short lived. Thus, methods of increasing the immune system recognition of and response to neoplastic cells are greatly needed.
One strategy to improve the efficacy of such vaccinations has included the use of non-specific adjuvants or immunostimulants such as BCG and Corynebacterium parvum. However, this has resulted in little improvement.
Another approach has been to increase the immunogenicity of tumor cells by treating the cells to be injected in different ways to enhance the exposure of their surface antigens. For example, U.S. Pat. No. 4,931,275 describes, using as a vaccine, cells treated with pressure or cholesteryl hemisuccinate, or using as vaccines plasma membranes or membrane proteins from these cells.
Another approach has focused on the interaction of cytokines and the immune system. Cytokines and combinations of cytokines have been shown to play an important role in the stimulation of the immune system. For example, U.S. Pat. No. 5,098,702, describes using combinations of TNF, IL-2 and IFN-β in synergistically effective amounts to combat existing tumors. U.S. Pat. No. 5,078,996 describes the activation of macrophage nonspecific tumoricidal activity by injecting recombinant GM-CSF to treat patients with tumors. However, because the doses of cytokines necessary to effect tumor development are often systemically toxic, direct treatment of patients is frequently not feasible (see, e.g., Asher et al., (1991) J. Immun. 146:3227-3234 and Havell et al., (1988) J. Exp. Med. 167:1067-1085).
To avoid such toxicity, non-neoplastic cells genetically modified to express a cytokine have been administered as vaccines. For example, autologous fibroblasts genetically modified to secrete IL-2 have been administered with a tumor antigen at a site other than an active tumor site. In a related approach, the fibroblast has been genetically modified to express both a cytokine and the tumor antigen (see, e.g., U.S. Pat. No. 5,674,486 Sobel, et al.).
In an alternative approach, tumor cells, themselves, have been genetically modified to express a cytokine. These vaccines have been used to potentiate tumor-associated antigen presentation to T cells of a subject. For example, studies have shown that the introduction of cytokine genes into murine tumor cells induced increased immunogenicity and decreased tumorigenesis (see, e.g., Gansbacher et al., (1990) Cancer Res. 50: 7820-7825; Fearon et al., (1990) Cell. 60:397-403; Ley et al., (1981) Eur. J. Immunol. 21:851-854; Watanabe et al., (1989) Proc. Natl. Acad. Sci. (USA) 86:9456; Gansbacher et al., (1990) J. Exp. Med. 172:1217-1224; Gansbacher et al., (1992) Proc. Am. Assoc. Cancer Res. 33:351; Tepper et al., (1989) Cell 57:503-512; Hock et al., (1991) J. Exp. Med. 174:1291-1298; and Porgador et al., (1992) Cancer Res. 52:3679). In addition, localized high concentrations of certain cytokines delivered by genetically modified cells have led to tumor regression in animals and humans (see, e.g., Gansbacher et al., (1990) Cancer Res., 50:7820-7825; Fornis et al., (1988) Cancer Met. Rev., 7:289-309; Fearon et al., (1990) Cell 60:397-403; and published GVAX® vaccine patent applications and patents), and in some cases, tumor immunity (Fearon et al., (1990) Cell 60:397-403). Thus, activating the immune system to respond to a tumor is a viable therapeutic alternative to irradiation and chemotherapy. Accordingly, improved, more efficacious activation methods specific for certain cancers are greatly needed.
One method of activating the immune system is to identify novel tumor-associated antigens such as tumor rejection antigens. U.S. Pat. No. 5,763,155 describes the identification of the MACE oncofetal family of tumor rejection antigens which are melanoma-associated. These antigens are recognized by host human T cells, but may not elicit an antibody response. Unfortunately, clinically relevant tumor rejection antigens for immune therapy for the treatment of most other types of cancer have not yet been identified.
Thus, the identification of clinically relevant, tumor-associated antigens is needed to provide improved methodologies for stimulating the immune system to recognize a tumor cell not normally targeted such that the tumor cell will elicit an effective cellular and serological or humoral response. Also needed are methods of screening for such antigens.